Laser beam scanning device

ABSTRACT

Scanning of a high power laser beam while it is being used is accomplished by deflecting the laser beam to its target with a polished metal mirror. Multiple thermocouple wires attached to the rear of the mirror provide temperature (and hence beam power) information at various points on the mirror. Scanning is achieved by means of a selector switch which sequentially samples the thermocouple outputs. The thermocouple output voltages are measured and recorded as a function of laser beam power.

mted States Pateu 11 1 1111 3,766,168 M n 1 1 June 12, 1973 LASER BEAMSCANNING DEVICE 3,118,061 1/1964 Bender 250/833 lnvemon Dennis N. nsealos Verdes 3,391,279 7/1968 Detrio 250/83.3

I Peninsula, Calif. 1 v

Primary Exammer-Herbert Goldstem [73] Assignee: The United States ofAmerica as Atmmey Harry Herbert JR and Willard represented by theSecretary of the Matthews, JR

Air Force [22] Filed: Nov. 16, 1971 ABSTRACT [21] Appl' 199184 Scanningof a high power laser beam while it is being used is accomplished bydeflecting the laser beam to its [52] U.S. Cl. 73/190 R, 250/833 HPtarget with a polished meta] mirror. Multiple thermo- [51] Int. Cl. G01k17/00 couple wires attached to the rear of the mirror provide [58] Fieldof Search 73/15, 190, 355; temperature (and hence beam power)information at 250/833 HP various points on the mirror. Scanning isachieved by means of a selector switch which sequentially samples [56]ReferencesCited the thermocouple outputs. The thermocouple output UNITEDSTATES PATENTS voltages are measured and recorded as a function of3,604,930 9/1971 Allen 250/833 laser beam Power 1 2,938,122 5/1960 Cole73/355 3,566,669 3/1971 Lawrence et a1. e 73/15 1 3 Drawmg F'gures3,622,245 11/1971 Rasmussen 73/190 3,368,076 2/1968 Clifford 250/833REFERENCE Ju/v r a/vs $54!: ran

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INVENTOR. DE N\S N- MHNSELL K MM.

ATTORNEYS 1 LASER BEAM SCANNING DEVICE apparatus for analyzing andmonitoring high power 5 laser beams.

It is often necessary and desirable to evaluate high power laser beamswhile the laser is in use. In other instances continuous monitoring ofoperational lasers is required. However, using currently know techniquesit is not possible to probe the cross section of a high power laser beamwithout inserting a screen or probe detector into the higher powerregion. These devices eventually distort, fracture, or even vaporize asbeam power is increased. Also the beam itself is usually distorted bythe interfering structures. There currently exists therefore the needfor apparatus capable of scanning and analyzing a high power laser beamthat can be used while the laser is in operation. It is also importantthat such apparatus is not destroyed by the laser beam when subjected toextended use and that it does not effect degradation or deterioration ofthe beam itself. The present invention is directed toward accomplishingthese and other ends.

SUMMARY OF THE INVENTION The apparatus of the present inventioncomprises a laser beam reflecting mirror to which is attached multiplethermocouple devices. The thermocouple devices are positioned on themirror in a uniformly spaced array such that the mirror is in effectdivided into zones. The output of any thermocouple device is a measureof the heating of the mirror by the portion of the laser beam beingreflected by the zone associated with that particular thermocoupledevice. The output voltage is, of course, also proportional to the powerof that particular portion of the laser beam. Scanning of the beam isaccomplished by a selector switch which sequentially samples the outputsof each thermocouple device in the array.

In a preferred embodiment of the invention the mirror is a polishedcopper plate and each thennocouple device is a bimetal elementconsisting of a constantan wire and the mirror itself.

It is a principal object of the invention to provide new and improvedapparatus for scanning a high power laser beam.

It is another object of the invention to provide apparatus for scanninga high power laser beam that can be used while the laser is in use.

It is another object of the invention to provide apparatus capable ofmonitoring and evaluating the beam power of an operational laser withoutdegrading the beam itself or interfering with its use.

These, together with other objects, features and advantages of theinvention will become more apparent from the following detaileddescription taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 2 illustrates in block diagram form thevarious components of the apparatus of the invention and theirrelationshipv to an operational laser;

FIG. 2 illustrate'sthe laser reflector mirror comprehended by theinvention together with a block diagram of associated components; and

FIG. 3 is a sectional view of the mirror of FIG. 2 taken at 3-3.

' DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The variouscomponents of the apparatus of the invention and their organization andrelationship to an operational laser are illustrated in FIG. 1. Laserbeam 5 generated by laser source 4 is directed to target 6 by means ofreflecting mirror 7. The outputs of a multiplicity of thermocoupledevices (not shown) are connected to reference junction 13 wherefromthey are se quentially sampled by selector. switch 8. These sampledoutputs are measured by measuring device 9 and then recorded ordisplayed on CRT display 15.

Mirror 7 and its associated thermocouple devices are illustrated in moredetail in FIGS. 2 and 3. Mirror 7 can advantageously be a thin copperplate having a highly polished surface 10. The thermocouple devices canbe constantan wires 12 prependicularly affixed to the rear of mirror 7by means of epoxy substrate 11. Each thermocouple device in thispresently preferred embodiment therefore consists of the two dissimilarmetals (the constantan wire and the copper mirror) and the referencejunction unit 13. Wire 14 connecting the mirror 7 to reference junction13 is of course also of copper. Although copper and constantan areindicated here as the thermocouple constituents any other suitabledissimilar metals could be used. Such a choice would depend uponengineering design requirements such as temperature range, beam power,and the like. The constantan wires 12 are arranged in a uniform array asillustrated by FIG. 3. Spacing between wires should be large compared tothe thickness of the copper plate to minimize the effect of heating fromadjacent zones. The wires can be sequentially scanned in any desiredorder by means of selector switch 8. Selector switch 8 can be totallyelectronic thus eliminating the need for moving parts and contactors.The outputs thus sampled are measured by measuring device 9. Any

means for measuring small voltages accurately can be used. Themillivoltmeter and the potentiometer are typical examples of such ameasuring device.

It will be understood that various changes in the detailed materials andarrangement of parts which have been herein described and illustrated inorder to explain the nature of the invention may be made by thoseskilled in the art without departing from the spirit and scope of theinvention as defined in the appended claims.

I claim:

1. Apparatus for scanning a high power laser beam comprising a mirroradapted to deflect a high power laser beam, said mirror comprising asingle thin copper plate having one highly polished reflecting surface,

a multiplicity of thermocouple devices operably engaged to the rear ofsaid mirror andarranged in a uniform array, the spacing between arraydevices being larger relative to the mirror plate thickness and adaptedto provide a substantially isolated temperature zone for each saidthermocouple device,

a selector switch adapted to sequentially sample the output voltage ofsaid thennocouple devices,

means for measuring the sampled thermocouple output voltages, and

meansfor recording the measured output voltages as a function of laserbeam power.

* 4' III I! l

1. Apparatus for scanning a high power laser beam comprising a mirroradapted to deflect a high power laser beam, said mirror comprising asingle thin copper plate having one highly polished reflecting surface,a multiplicity of thermocouple devices operably engaged to the rear ofsaid mirror and arranged in a uniform array, the spacing between arraydevices being larger relative to the mirror plate thickness and adaptedto provide a substantially isolated temperature zone for each saidthermocouple device, a selector switch adapted to sequentially samplethe output voltage of said thermocouple devices, means for measuring thesampled thermocouple output voltages, and means for recording themeasured output voltages as a function of laser beam power.